Advancements in communication technologies have permitted the development, and deployment, of many varied types of communication systems by which to effectuate the communication of data. For instance, multi-user radio communication systems are available, and widely used, through which to communicate pursuant to effectuation of a communication service. A cellular communication system is exemplary of a multi-user radio communication system. Voice, and other, data generated during operation of a cellular, as well as other radio, communication systems is communicated upon radio communication channels defined upon portions of the electromagnetic spectrum.
A cellular communication system is deployed through the installation of a network infrastructure with which mobile stations communicate. The network infrastructure is installed throughout a geographical area that is to be encompassed by the communication system. In a conventional deployment, the network infrastructure includes a plurality of spaced apart radio base stations. Groups of the radio base stations are coupled to control devices, sometimes referred to as base station controllers. The control devices operate, amongst other things, to control various functions of the radio base stations with which the control devices are coupled. And, groups of the control devices are, in turn, coupled to mobile switching centers and gateway mobile switching centers (MSC/GMSCs). Switching, and other connection, operations are performed by such entities to effectuate communication of data with external networks.
Each radio base station defines a geographical area, referred to as a cell, and from which a cellular communication system derives its name. A cell is a portion of the geographical area encompassed by the cellular communication system, positioned proximate to a radio base station. During normal operation of the cellular communication system, a mobile station is able to communicate with the base station that defines the cell in which the mobile station is located.
The frequency bandwidth allocated for communications in a cellular communication system is efficiently utilized. Due to the positioning of the radio base stations at the spaced positions throughout a geographical area, only relatively power signals need to be generated to effectuate communications between a mobile station and a radio base station. The same channels can thereby be reused by different ones of the radio base stations. A cell reuse plan is utilized to allocate channels to different ones of the radio base stations in a manner to minimize interference between concurrently used channels.
Due to the inherent mobility of a mobile station, and the use of relatively low powered signals to effectuate communications between a radio base station and a mobile station, the mobile station might not be able to continue to communicate with a radio base station with which communications are initiated. More particularly, as a mobile station passes from cell to cell, the mobile station must communicate with successive ones of the radio base stations. Communications with the mobile station continue, thereby, as the mobile station passes through the successive cells defined by the successive ones of the base stations.
Transfer of communications with the mobile station from one radio base station to another is referred to as a communication handoff, or handover. The radio base station from which the communications are banded off is referred to as a serving, or active, cell site, and the base station to which communications are at least potentially to be handed off is referred to as a target cell site. Handover of communications and the procedures leading up to the handover of communications is a fairly complex procedure. Determinations must be made that a handover should occur and a determination to which radio base station to which to handover communications must also be made.
In a cellular communication system that utilizes code division multiple access (CDMA) techniques, a procedure, referred to as a soft handoff, is performed to effectuate handover of communications from a serving cell site to a target cell site. In a soft handover procedure, communications are handed off from a serving cell site to a target cell site without need for the mobile station to retune to a different channel. In other cellular communication systems, hard handoffs are performed in which the mobile station tunes to a different channel pursuant to the handoff of communications.
In any handover procedure, and particularly in a soft handover procedure performed in a CDMA communication system, measurements are made at the mobile station to determine whether a handoff of communications is needed. In a CDMA communication system, for instance, pilot signals are broadcast by the radio base stations. Separate ones of the radio base stations transmit separate pilot signals. The mobile station monitors the pilot signals transmitted by the active cell site as well as one or more potential target cell sites. Measurements are taken of signal indicia associated with the pilot signals. And, responsive thereto, decisions are made whether to initiate handover procedures. In order to maintain the correct base stations for soft handoffs, timely and accurate estimation of the signal strengths, or other indicia of the pilot signals, when detected by the mobile station, must be made. And, decisions related to whether to drop a base station from a soft handoff analysis as a potential target base station, an erroneous decision should not be made due to measurements made during deep fading conditions.
The receive circuitry of the mobile station includes various circuit elements through which representations of the received pilot signals are passed during receive circuitry operations. A filter element is amongst the elements of the receive circuitry that operates upon the representations of the pilot signals monitored by, and operated upon, the receive circuitry during its operation. The filter element exhibits a filter response time that is related, amongst other things, to its gain.
There is a need, however, quickly to make handoff decisions, a filter exhibiting a lengthy response time is contrary to the ability the quick decisions. However, during poor signal conditions, such as during deep fading conditions, a fast response time, and associated small filter gain, does not adequately permit measurement of the pilot signal indicia.
If a manner could be provided by which dynamically to select the filter characteristics of the filter element, improved handover procedures would be possible. When signal conditions are good, a decreased response time of the filter element would be selected to optimize the speed of operation of the receive circuitry pursuant to the handover analysis procedure. And, when signal conditions are poor, the filter characteristics of the filter element would be selected to increase the gain of the filter to permit a more lengthy analysis of the pilot signal indicia.
It is in light of this background information related to filter element selection in a receive circuit of a communication station operable in a cellular, or other radio, communication system, that the significant improvements of the present invention have evolved.